This invention relates to a key switch operation detection device capable of efficiently detecting operations of a number of key switches.
Various proposals have been made for detecting an operating state(making or breaking) of one or more key switches provided in a device such as a keyboard of an electronic musical instrument which has a large number of key switches.
There is a conventional device in which conductors are individually connected to respective key switches and outputs delivered on these conductors are individually detected. This device requires a complicated wiring and therefore is uneconomical. Besides, this device requires a large number of connection terminals for connecting such wiring to a circuit utilizing the result of detection of the key switch states so that it is unsuited for a circuit design employing a semiconductor integrated circuit in which the number of connection pins available for use is limited.
There is another proposal according to which key switches are arranged in a matrix circuit so that each of these key switches will be identified by a column line (input line) and a row line (output line) on which the key switch is disposed and an operating state of each key switch is detected by sequentially scanning all of the key switches. Such proposal is disclosed in the issued U.S. Pat. No. 3,882,751. The proposed device is advantageous in that the number of conductors to be connected between the outside circuit and the key switches can be saved. This device, however, has a problem that an undesirable time delay sometimes occurs between the actual making or breaking of the key switches and detection thereof because all of the key switches must be scanned one by one. Further, time required for detecting the states of all of the key switches is fixed depending upon the scanning speed so that if there are only a few key switches in operation among a large number of key switches, a substantial waste of time occurs due to the fixed time for detection. To reduce such waste of time, the rate of the clock used in the system must be increased with resulting adverse effects on the system such as increase in the power consumption.
With a view to improving the disadvantages in the above described proposal, the applicant has proposed novel key switch detection systems in its issued U.S. Pat. No. 3,899,951 and copending application Ser. No. 602631 now U.S. Pat. No. 4,033,221. These systems basically depend upon scanning of a key switch matrix circuit to detect the operating or nonoperating state of the key switches and the improvement resides in providing a device for reducing the scanning time by scanning only necessary sections from among all the key switches. Such improvement has succeeded only in reduction of the scanning time, but yet the unavoidable waste of time inherent in the scanning systems has remained unsettled. Even if the scanning section is limited only to necessary section(s) in the above scanning systems, the probability that the switches in a nonoperating state are included in the scanning section(s) is fairly high. Accordingly, such nonoperating key switches must be equally scanned and waste of time still occurs.
Furthermore, if a low rate clock is desirable in a circuit utilizing the result of detection of the key switches for reasons of simplification of the circuit design, reduction of power consumption and reduction of manufacturing costs, the above described waste of time accompanying the scanning system must be eliminated. The prior art scanning system apparently has limitations in eliminating such waste of time.